/INTER/TYPE5
Block Format Keyword This interface is used to simulate impacts between a main surface and a list of secondary nodes.
Description
 Simulate impact of beam truss spring nodes on a surface
 Simulate impact of a complex fine mesh on a simply convex surface
 Replace a rigid wall
See main limitations of this interface in Comment 1.
Format
(1)  (2)  (3)  (4)  (5)  (6)  (7)  (8)  (9)  (10) 

/INTER/TYPE5/inter_ID/unit_ID  
inter_title  
grnd_ID_{s}  surf_ID_{m}  I_{bag}  I_{del}  
Stfac  Fric  Gap  T_{start}  T_{stop}  
I_{BC}  I_{Rm}  Inacti  
I_{fric}  I_{filtr}  X_{freq}  sens_ID  ${P}_{tlim}$ 
(1)  (2)  (3)  (4)  (5)  (6)  (7)  (8)  (9)  (10) 

C_{1}  C_{2}  C_{3}  C_{4}  C_{5} 
(1)  (2)  (3)  (4)  (5)  (6)  (7)  (8)  (9)  (10) 

C_{6} 
Definitions
Field  Contents  SI Unit Example 

inter_ID  Interface
identifier (Integer, maximum 10 digits) 

unit_ID  Unit identifier (Integer, maximum 10 digits) 

inter_title  Interface
title (Character, maximum 100 characters) 

grnd_ID_{s}  Secondary nodes group
identifier. (Integer) 

surf_ID_{m}  Main surface
identifier. (Integer) 

I_{bag}  Airbag vent holes closure
flag in case of contact.
(Integer) 

I_{del}  Node and segment deletion
flag. 5
(Integer) 

Stfac  Interface stiffness scale
factor. Default = 0.2 (Real) 
$\left[\frac{\text{N}}{\text{m}}\right]$ 
Fric  Coulomb
friction. (Real) 

Gap  Gap for impact
activation. (Real) 
$\left[\text{m}\right]$ 
T_{start}  Start time for contact
impact computation. (Real) 
$\left[\text{s}\right]$ 
T_{stop}  Time for temporary
deactivation. (Real) 
$\left[\text{s}\right]$ 
I_{BC}  Deactivation flag of
boundary conditions at impact. (Boolean) 

I_{Rm}  Renumbering flag for
segments of the main surface.
(Integer) 

Inacti  Removing the initial
penetrations flag. 12
(Integer) 

I_{fric}  Friction formulation flag.
9
(Integer) 

I_{filtr}  Friction filtering flag.
10
(Integer) 

X_{freq}  Filtering coefficient.
Should have a value between 0 and 1. (Real) 

sens_ID  Sensor identifier to
activate/deactivate the interface. If an identifier sensor is defined, the activation/deactivation of interface is based on sensor and not on T_{start} or T_{stop}. (Integer) 

${P}_{tlim}$  Maximum tangential
pressure. 13
Generally ${P}_{tlim}$ is defined as yield stress. Default = 10^{30} (Real) 
$\left[\text{Pa}\right]$ 
C_{1}  Friction law
coefficient (Real) 

C_{2}  Friction law
coefficient (Real) 

C_{3}  Friction law
coefficient (Real) 

C_{4}  Friction law
coefficient (Real) 

C_{5}  Friction law
coefficient (Real) 

C_{6}  Friction law
coefficient (Real) 
Flags for Deactivation of Boundary Conditions: IBC
(1)1  (1)2  (1)3  (1)4  (1)5  (1)6  (1)7  (1)8 

I_{BCX}  I_{BCY}  I_{BCZ} 
Definitions
Field  Contents  SI Unit Example 

I_{BCX} 
(Boolean) 

I_{BCY} 
(Boolean) 

I_{BCZ} 
(Boolean) 
Comments
 The main limitations for this
interface are:
 The main segment normals must be oriented from main surface to the secondary nodes;
 On the main side, the segments must be connected to solid or shell elements;
 The same node may not be put in the two impact surfaces;
 Some search problems (see Common Problems in the Radioss Theory Manual).
 All the normals of the main surface segments must be oriented toward the secondary surface. Otherwise, mixing the orientation of the normals can lead to initial penetrations.
 Secondary and main surfaces should be topologically different: a node cannot be on the two surfaces at the same time.
 Flag I_{del} =1 has a CPU cost higher than I_{del} =2.
 If the stiffness on the main side is much less than the stiffness on the secondary side, the stiffness factor Stfac can be increased to a value greater than 1; otherwise the stiffness factor should have a value between 0 and 1.
 For example, the interface
stiffness balance is:
(1) $$\mathit{Stfac}\le \frac{{E}_{s}\cdot {e}_{s}}{{E}_{m}\cdot {e}_{m}}$$Where, ${E}_{m}$
 Main stiffness
 ${e}_{m}$
 Main thickness
 ${E}_{s}$
 Secondary stiffness
 ${e}_{s}$
 Secondary thickness
 If I_{BCX} = 1, the boundary condition in X direction is deactivated. I_{BCY} and I_{BCZ} behave the same way respectively in Y and Z direction.
 Boundary conditions are only deactivated on secondary nodes.
 For friction formulation:
 If the friction flag I_{fric} > 0
(default), the old static friction formulation is used:
${F}_{T}\le \mu \cdot {F}_{N}$ with $\mu =\mathit{Fric}$ (Coulomb friction).
 If the friction flag I_{fric} > 0, new
friction models are introduced. In this case, the friction coefficient
is set by a function:
(2) $$\mu =\text{\mu}\left(p,V\right)$$Where, $p$
 Pressure of the normal force on the main segment
 $V$
 Tangential velocity of the secondary node relative to the main segment
Currently, the following formulations are available: I_{fric} = 1
(Generalized viscous friction law):
(3) $$\mu =\mathit{Fric}+{C}_{1}.p+{C}_{2}\cdot V+{C}_{3}.p\cdot V+{C}_{4}\cdot {p}^{2}+{C}_{5}\cdot {V}^{2}$$  I_{fric} = 2
(Modified Darmstad law):
(4) $$\mu =Fric+{C}_{1}\cdot {e}^{\left({C}_{2}V\right)}\cdot {p}^{2}+{C}_{3}\cdot {e}^{\left({C}_{4}V\right)}\cdot p+{C}_{5}\cdot {e}^{\left({C}_{6}V\right)}$$  I_{fric} = 3
(Renard law):
(5) $$\mu ={C}_{1}+\left({C}_{3}{C}_{1}\right)\cdot \frac{V}{{C}_{5}}\cdot \left(2\frac{V}{{C}_{5}}\right)$$if $V\in \left[0,{C}_{5}\right]$(6) $$\mu ={C}_{3}\left(\left({C}_{3}{C}_{4}\right)\cdot {\left(\frac{V{C}_{5}}{{C}_{6}{C}_{5}}\right)}^{2}\cdot \left(32\cdot \frac{V{C}_{5}}{{C}_{6}{C}_{5}}\right)\right)$$if $V\in \left[{C}_{5},{C}_{6}\right]$(7) $$\mu ={C}_{2}\frac{1}{\frac{1}{{C}_{2}{C}_{4}}+{\left(V{C}_{6}\right)}^{2}}$$if $V\ge {C}_{6}$
Where,
${C}_{1}={\mu}_{s}$
${C}_{2}={\mu}_{d}$
${C}_{3}={\mu}_{\mathrm{max}}$
${C}_{4}={\mu}_{\mathrm{min}}$
${C}_{5}={V}_{cr1}$
${C}_{6}={V}_{cr2}$
First critical velocity ${V}_{cr1}={C}_{5}$ must be different to 0 ( ${C}_{5}\ne 0$ ).
First critical velocity ${V}_{cr1}={C}_{5}$ must be less than the second critical velocity ${V}_{\mathit{cr}2}={C}_{6}({C}_{5}<{C}_{6})$ .
The static friction coefficient C_{1} and the dynamic friction coefficient C_{2}, must be less than the maximum friction C_{3} ( ${C}_{1}\le {C}_{3}$ and ${C}_{2}\le {C}_{3}$ ).
The minimum friction coefficient C_{4} must be less than the static friction coefficient C_{1} and the dynamic friction coefficient C_{2} ( ${C}_{4}\le {C}_{1}$ and ${C}_{4}\le {C}_{2}$ ).Table 1. Units for Friction Formulations I_{fric} Fric C_{1} C_{2} C_{3} C_{4} C_{5} C_{6} 1 $\left[\frac{1}{\text{P}\text{a}}\right]$ $\left[\frac{\text{s}}{\text{m}}\right]$ $\left[\frac{\text{s}}{\text{Pa}\cdot \text{m}}\right]$ $\left[\frac{1}{{\text{Pa}}^{2}}\right]$ $\left[\frac{{\text{s}}^{2}}{{\text{m}}^{2}}\right]$ 2 $\left[\frac{\text{s}}{\text{m}}\right]$ $\left[\frac{\text{s}}{\text{m}}\right]$ $\left[\frac{\text{s}}{\text{m}}\right]$ 3 $\left[\frac{\text{m}}{\text{s}}\right]$ $\left[\frac{\text{m}}{\text{s}}\right]$  If the friction flag I_{fric} > 0
(default), the old static friction formulation is used:
 If I_{filtr} flag is not zero, the tangential
forces are smoothed using a filter:
(8) $${F}_{T}=\alpha \cdot {{F}^{\prime}}_{T}+\left(1\alpha \right)\cdot {{{F}^{\prime}}_{T}}^{1}$$Where, α coefficient is calculated from:
if I_{filtr} =1 ➤ $\alpha ={X}_{freq}$ , simple numerical filter
if I_{filtr} =2 ➤ $\alpha =\frac{2\cdot \pi}{{X}_{freq}}$ , standard 3dB filter, with ${X}_{freq}=\frac{dt}{T}$ , and T = filtering period
if I_{filtr} =3 ➤ $\alpha =2\cdot \pi \cdot {X}_{freq}\cdot dt$ standard 3dB filter, with X_{freq} = cutting frequency
 The coefficients C_{1} through C_{6} are used to define a variable friction coefficient $\mu $ for new friction formulations.
 Since the coordinate change
will be irreversible, this action needs be made with great precaution because it
may:
 Create other initial penetrations, if several surface layers are defined in the interfaces
 Create initial energy if node belongs to spring element
Inacti = 3 or 4 is only recommended for small initial penetrations.
 In 2D analysis, tangent contact force is
limited when
${P}_{tlim}$
is defined by the following
equation:
(9) $${F}_{t}\le {P}_{tlim}\frac{S}{\sqrt{3}}$$While, $S$ is extrapolated length of segments connected to the secondary node.